The FBI said it had infiltrated online "carder" forums hosted on the DarkMarket.ws Web site, which was widely used by online scammers to buy and sell stolen credit card numbers, other financial information, and even the devices used to make fake banking cards. Before it was shut down earlier this month, the Web site had registered more than 2,500 members.

The FBI ran its sting in cooperation with the U.K.'s Serious Organized Crime Agency and authorities in Turkey and Germany. "The arrests this week in the U.K. are a good demonstration of the coordination taking place today between the FBI, the Serious Organized Crime Agency... and other law enforcement agencies around the globe," FBI Cyber Division Assistant Director Shawn Henry said Thursday in a statement.

In addition to the drawing the 56 arrests, the sting helped the FBI seize compromised accounts and prevent the loss of about US$70 million in fraud, the FBI said. It has also generated new leads that are being tracked down by international law enforcement.

Dark Market's members have had a lot to be nervous about this week.

Although Dark Market was thought to have been administered by a criminal going by the name Master Splyntr, German Public Radio reported on Monday that the FBI had been running a sting operation on the site since late 2006, and that Master Splyntr was actually an FBI agent named J. Keith Mularski.

The FBI did not respond to requests for further comment on this story.

According to a report in Wired News, Master Splyntr announced that Dark Market would be closing last month after one of the Web site's administrators, Cha0, was arrested in Turkey after "reportedly kidnapping and torturing a police informant."

"It is apparent that this forum &#8230; is attracting too much attention from a lot of the world services (agents of FBI, SS, and Interpol)," Wired quotes Master Splyntr as writing in a forum post. "I guess it was only time before this would happen. It is very unfortunate that we have come to this situation, because ... we have established DM as the premier English speaking forum for conducting business. Such is life. When you are on top, people try to bring you down."

To comment on this article and other PCWorld content, visit our Facebook page or our Twitter feed.